1. Field of the Invention
The present invention relates to semiconductor wafer cleaning and, more particularly, to techniques for applying fluids over a cleaning brush and improving wafer cleaning throughput and efficiency.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well-known that there is a need to clean a wafer where a fabrication operation has been performed that leaves unwanted residuals on the surface of the wafer. Examples of such a fabrication operation include plasma etching (e.g., tungsten etch back (WEB)) and chemical mechanical polishing (CMP). If left on the surface of the wafer for subsequent fabrication operations, the unwanted residual material and particles may cause, among other things, defects such as scratches on the wafer surface and inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is therefore necessary to clean the wafer adequately yet efficiently after fabrication operations that leave unwanted residue on the surface of the wafer.
FIG. 1A shows a high level schematic diagram of a wafer cleaning system 50. The cleaning system 50 typically includes a load station 10 where a plurality of wafers in a cassette 14 may be inserted for cleaning through the system. Once the wafers are inserted into the load station 10, a wafer 12 may be taken from the cassette 14 and moved into a brush station one 16a, where the wafer 12 is scrubbed with selected chemicals and water (e.g., de-ionized (DI) water). The wafer 12 is then moved to a brush station two 16b. After the wafer has been scrubbed in brush station 16, the wafer is moved into a spin, rinse, and dry (SRD) station 20 where DI water is sprayed onto the surface of the wafer and spun to dry. During the rinsing operation in the SRD station, the wafer rotates at about 100 rotations per minute or more. After the wafer has been placed through the SRD station 20, the wafer is moved to an unload station 22.
FIG. 1B shows a simplified view of a cleaning process performed in a brush station 16. In brush station 16, the wafer 12 is inserted between a top brush 30a and a bottom brush 30b with top surface 12a facing up. The wafer 12 is capable of being rotated with rollers (not shown) to enable the rotating brushes 30a and 30b to adequately clean the entire top and bottom surfaces of the wafer 12. In certain circumstances, the bottom surface of the wafer is required to be cleaned as well because contaminants from the bottom may migrate to the top surface 12a. Although both the top surface 12a and the bottom surface of the wafer 12 are scrubbed with the brushes 30, the top surface 12a that is scrubbed with the top brush 30a is the primary surface targeted for cleaning, since the top surface 12a is where the integrated circuit devices are being fabricated. To more effectively clean the wafer 12, a cleaning solution can be applied onto the top brush 30a by the use of a drip manifold 13a. In this example, the drip manifold 13a is attached to a drip control 13 which is in turn connected to a fluid source 24. The fluid source 24 pumps fluid (e.g., any cleaning chemical or DI water) through the fluid control 13 which controls the amount of fluid entering the drip manifold 13a. After receiving the fluid from the fluid control 13, the drip manifold 13a then expels a non-uniform drip 32 onto the top brush 30a. As will be discussed below, this non-uniform drip 32 has been observed to cause problems in cleaning operations.
FIG. 1C shows a cross sectional view of the elements depicted in FIG. 1B. When the wafer 12 has been placed on the bottom brush 30b, the top brush 30a is lowered onto the wafer 12. As the top brush 30a is lowered onto the wafer 12, drip control 13 starts the flow of fluid to the drip manifold 13a which releases the non-uniform drip onto the top brush 30a. During this time, both the bottom brush 30a and 30b turn to create the mechanical scrubbing action.
FIG. 1D shows a more detailed side view of the wafer cleaning structure depicted in FIG. 1B. In general, it is a goal to have the fluid provided to the drip manifold 13a expel xe2x80x9cdropletsxe2x80x9d of fluid evenly over the entire length of the brush 32a. To do this, it is common practice to introduce the fluid into the drip manifold 13a at reduced flow rates and pressures. To accomplish this, the fluid source 24 supplies the cleaning fluid through the drip control 13 which regulates the amount of fluid injected into a near end 31a of the drip manifold 13a. Unfortunately, as the fluid enters into the near end 31a, the fluid tends to flow out of the drip manifold faster at that end than at a far end 31b. This differential fluid expulsion occurs because most of the fluid is released through the drip holes at the near end 31a before the fluid can reach the drip holes at the far end 31b. Therefore, if the drip manifold 13a were totally horizontal, more near end drops 32a will be expelled than far end drops 32b. In the prior art, the drip manifold 13a was sometimes tilted downward slightly at a manifold angle Ø 42 to allow more fluid to reach the far end 31b. The manifold angle 42 is determined by finding the optimal angle of the drip manifold 13a which produces the equivalent amount of drip from both the near end 31a and the far end 31b. This manifold angle 42 is measured relative to a y-axis 40a and an x-axis 40b. As the drip manifold 13a expels the far end drops 32a and near end drops 32b onto the top brush 30a, the brushes 30 turn to scrub the wafer 12.
Unfortunately, calibrating the drip manifold 13a to produce the right amount of fluid flow can be a very time consuming and a difficult process. By guesswork and trial and error, numerous manifold angles Ø 42 must be tried to find the optimal flow rate of the cleaning fluid. Even after the optimal flow rate has been found, the drip manifold may need re-calibrating every time the cleaning apparatus is moved to another location. This problem occurs because each different location (even a different section of the same room) can have a floor angle that is different from the previous location. Therefore, as is often the case, if the cleaning apparatus must be moved frequently, the need for constant re-calibration can create large wastes of time and reduce wafer cleaning throughput. In addition, further problems in the maintenance of manifold angle Ø 42 may occur if the drip manifold is moved by a bump or nudging of the cleaning apparatus because even a slight movement of the drip manifold can have the effect of altering the manifold angle Ø 42. Therefore, the prior art drip manifold 13a must often be re-calibrated far more often than is desirable or practical.
FIG. 1E depicts a more detailed cross-sectional view of the drip manifold 13a which is expelling the non-uniform drip 32 through a drip hole 13b. As is common practice, the drip hole 13b is formed by drilling a hole into the drip manifold 13a. Unfortunately, the drilling process is known to leave hole shavings 13c in and around the drip holes 13b. These shavings can potentially be introduced over wafers as particulates causing damage to circuits or retard the flow of fluid, thus causing un-even fluid sprays along the drip manifold 13a. To compensate for potential hole shavings 13c and un-even fluid delivery, it is common practice to deliver fluids to the drip manifold 13a at high pressures and flow rates. This is believed to improve the distribution of fluid out of all of the drip holes 13b along the drip manifold 13a. As consequence, however, this high pressure delivery and flows tend to produce high pressure jets 32xe2x80x2.
Although the distribution of fluids out of the drip holes 13b improved, the high pressure jets 32xe2x80x2 have the disadvantageous effects of damaging the delicate surface of the brush 32a. In some cases, after relatively few cleaning operations, it was noticed that the brush 32a became somewhat shredded or frayed. Consequently, the solution of simply increasing fluid delivery flow and pressures caused additional problems beyond those of un-even fluid delivery.
Because of these inherent problems in the present drip manifold 13a, additional devices such as pressure regulators, pressure gauges, and flow meters, which are part of the drip control 13, have been used in a largely unsuccessful attempt to prevent over spraying. Unfortunately, even with seemingly proper drip control, unforeseen fluctuations in fluid pressure can occur which may result in the high pressure jet 32xe2x80x2 which have been known to damage the top brush 30a and/or the wafer 12.
It should be apparent that using the aforementioned drip manifold is unduly inefficient. Such a drip manifold has the downside of taking more time to setup, and requiring a large amount of maintenance time to keep the drip manifold at the perfect manifold angle Ø 42. Moreover, the fluid application must be carefully monitored because of the possible damage to brushes and wafers caused by flow altering effects of fluctuations in fluid pressure and hole shavings 13c. Therefore, using prior art dripping mechanisms can cause lower throughput of wafer cleaning and/or cause damage to the brushes and wafers.
In view of the foregoing, there is a need for a drip manifold that avoids the problems of the prior art by improving cleaning fluid dripping and increasing wafer cleaning efficiency and output.
Broadly speaking, the present invention fills these needs by providing an improved method for providing uniform chemical delivery over brushes of a wafer cleaning system. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a method for cleaning a wafer with a drip nozzle being configured for use in a drip manifold that is oriented over a brush of a wafer cleaning system is provided. The drip nozzle has a first end and a second end with a passage defined there between where the passage includes a wall that extends longitudinally between the first end and the second end. An orifice is defined within the passage and located at the first end of the drip nozzle. The method includes inputting a fluid into the drip nozzle at an acute angle relative to a longitudinal extension of the wall and reflecting the fluid stream off an internal wall of the drip nozzle at least twice in a direction that is toward the second end. The method further includes outputting at least one substantially uniform drop from the second end of the passage.
In another embodiment, a method for cleaning a wafer with a manifold including at least one drip nozzle is provided. The method includes inputting a fluid into a first end of the at least one drip nozzle at an acute angle relative to a wall that extends longitudinally between the first end and a second end of the at least drip nozzle. The method further includes reflecting the fluid stream off an internal wall of the at least one drip nozzle at least twice in a direction that is toward the second end of the at least one drip nozzle. The method also includes outputting at least one substantially uniform drop from the second end of the passage at a consistent rate, and applying the at least one substantially uniform drop onto a brush.
In yet another embodiment, a method for cleaning a wafer with a manifold including at least one drip nozzle is provided. The method includes inputting a fluid into a first end of the drip nozzle at an acute angle relative to a wall that extends longitudinally between the first end and a second end of the drip nozzle and reflecting the fluid stream off an internal wall of the drip nozzle at least twice in a direction that is toward the second end of the drip nozzle. The method also includes outputting at least one substantially uniform drop from the second end of the passage at a consistent rate and applying the at least one substantially uniform drop onto a brush. The method further includes scrubbing a wafer with the brush.
The advantages of the present invention are numerous. Most notably, by designing a drip manifold which produces consistent dripping of uniform drops, the wafer cleaning efficiency and throughput may be improved. The claimed invention removes the problems of variable cleaning chemical flow which causes problems such as brush and/or wafer damage.
The present drip manifold does not have to be oriented at a specific manifold angle to properly apply the cleaning fluid in the proper manner. This advancement obviates the need for continual re-calibrations of drip manifold systems to obtain and maintain the perfect manifold angle. This feature reduces time spent on maintaining the drip manifold and allows increased wafer cleaning throughput. Moreover, the present drip manifold is nearly immune to fluctuations in cleaning fluid dripped caused by small fluid pressure variations. Further, due to the design of the drip nozzle, flow alterations normally caused by hole shavings are also eliminated. Therefore the drip manifold will allow new drip systems to more easily produce and maintain the type of dripping preferable in the wafer cleaning process.
Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principle invention.